Repotting the bonsai?

I try re-potting 4 to 5 different fruit's bonsai trees i.e. Orange, Lemon, Mango but every time the tree die. I don't know what is I am doing wrong?

1st Method: When I see the tree pot is fill with roots then take off the tree from the pot and cut all the thick roots and remove some soil around the tree and then put it center on new pot having layer of soil containing this size O of rocks and then put the mixture of compost and this size of O of rocks around it.

2nd Method: When I see the tree pot is fill with roots then take off the tree from the pot and cut all the thick roots and remove all soil of the tree and then put it center on new pot having layer of soil containing this size O of rocks and then put the mixture of compost and this size of O of rocks around it.

3rd Method: When I see the tree pot is fill with roots then take off the tree from the pot and cut all the thick roots only and then put it center on new pot having layer of soil containing this size O of rocks and then put the mixture of compost and this size of O of rocks around it.